1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for controlling transmission power in a wireless communication system.
2. Related Art
Effective transmission/reception methods and utilizations have been proposed for a broadband wireless communication system to maximize efficiency of radio resources. An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference (ISI) with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference.
When a system uses the OFDM as a modulation scheme, orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users. In the OFDMA, frequency resources (i.e., subcarriers) are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner. In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers. In addition, a spatial multiplexing scheme using multiple antennas can be used to increase efficiency of a spatial domain.
An uplink control information (UCI) can be transmitted through an uplink control channel, i.e., a physical uplink control channel (PUCCH). The UCI may include various types of information such as a scheduling request (SR), an acknowledgement/non-acknowledgement (ACK/NACK) for a hybrid automatic repeat request (HARQ), a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), etc. The PUCCH carries various types of control information according to a format. Transmission of the UCI through the PUCCH may be found in the section 10 of 3rd generation partnership project (3GPP) TS 36.213 V8.8.0 (2009-09).
Meanwhile, a carrier aggregation (CA) system implies a system which supports a broadband by aggregating one or more carriers having a bandwidth narrower than that of a desired broadband when a wireless communication system intends to support the broadband. In the CA system, a user equipment can simultaneously transmit or receive one or a plurality of carriers according to capacity. The conventional transmission technique can be newly defined in the CA system. The CA system may be found in 3GPP TR 36.815 V9.0.0 (2010-3).
In a carrier aggregation system, a user equipment (UE) can periodically transmit the UCI through a plurality of component carriers (CCs), or can aperiodically transmit the CQI. In this case, maximum transmission power of the UE can be limited, and the UE can allocate and/or control power for each UL transmission channel, i.e., a PUCCH and a physical uplink shared channel (PUSCH).
There is a need for a method for properly allocating power for each UL channel.